On 7/31/2010 12:45 PM, Matti Aarnio wrote:
>> What? Is my APRS digipeater code wrong as it treats all WIDEn-N
> constructs the same and does dupe suppression on them all?
Under the current "New Paradigm" standards, WIDE1-1 _*IS*_ treated
differently from higher orders of N-N
The whole WIDE1-1, WIDE2-1 construct was invented (it was my proposal years
ago) to work around the "brain-dead" firmware limitations in Kantronics KPC3
TNCs. These TNCs are by far the most widely-used piece of hardware for
stand-alone digis without a computer in the US. [It's hard to beat the
simplicity and low power consumption (15mA at 12 VDC) of a KPC3+radio digi at a
remote site.] The problem is that KPCs do dupe suppression on WIDEn-N paths
but NOT on plain RELAY or plain WIDE.
On the other hand, many home users operating first-tier low-level digipeaters
(that in the past responded to "RELAY") use old TNCs (such as PK-232s, TAPR
TNC-2s, MFJ 1270s, etc) that do not have APRS-aware firmware in them. These
older devices _CAN NOT_ do n-N decremented SSIDs.
With rapid APRS growth in the early '2000s, the volume of unnecessary APRS
traffic due to RELAY and plain WIDE not supporting dupe checking just
exploded. A lot of discussion followed on how one could migrate to an
exclusively WIDEn-N network (with effective dupe control) while still
allowing non-N-N-aware home fill-in digis to remain part of the APRS
infrastructure. At the same time, one wanted to prevent home digis from acting
on anything but the very first hop of a path.
The solution was the two-part WIDE1-1,WIDE2-n path I proposed.
All home low-level digis set WIDE1-1 as a simple alias to be treated as an
ordinary callsign of WIDE1 with an SSID of -1. When a "dumb" home digi hears
WIDE1-1 as the first hop in a path, it digipeats it just like any other fixed
callsign, marks it as used, and passes the second WIDE2-1 or WIDE2-2 part
onward to the next tier of "real" N-N digis. (The home digis completely
ignore WIDE2-anything or higher since only WIDE1-1 is set as an alias to
digipeat on.)
True high-level WIDEn-N will respond to any value of WIDEn. If a high-level
digi (that DOES have proper WIDEn-N support) happens to hear the initial
transmission, it will process WIDE1-1 as a decremented n-N, mark it used up and
hand the second half WIDE2-n to the next (high-level) digipeater(s).
The difference when monitored off the air after the first hop is that a home
fill-in digipeat of the first hop would yield
WA8LMF to APRS via WIDE1-1*,WIDE2-1
while a first hop captured by a "real" decrementing WIDEn-N digi, would produce
WA8LMF to APRS via WIDE1-0*,WIDE2-1
or possibly
WA8LMF to APRS via *WIDE1*,WIDE2-1
if the monitoring TNC's firmware treats an SSID of "zero" as effectively no
SSID at all for display purposes.
The low-level WIDE1-1 home digis far outnumber the WIDE2-n "true wides".
Beaconing WIDE1-1 as the first hop from aircraft (that have a range of hundreds
of miles/km line-of-site) can potentially trigger hundreds of home WIDE1-1
digis simultaneously, when then ALL retransmit to the nearest true WIDEn-N
systems. If the first hop from an airborne station is a WIDE2-n only (which
the home digis just ignore) a few "true wides" rather than hundreds of home
stations will be triggered.
Yes, the whole scheme is a kludge to work around the limitations of 20-year-old
"clunker" TNC hardware, but it does kinda' sorta' work.........
-------------------------------------------------------------------------------
--
Stephen H. Smith wa8lmf (at) aol.com
EchoLink Node: WA8LMF or 14400 [Think bottom of the 2M band]
Skype: WA8LMF
Home Page: http://wa8lmf.net
NEW! *** HF APRS over PSK63 ***
http://wa8lmf.net/APRS_PSK63/index.htm
Universal HF/VHF/UHF Antenna Mounting System
http://wa8lmf.net/mobile/UniversalAntMountSystem.htm
"APRS 101" Explanation of APRS Path Selection & Digipeating
http://wa8lmf.net/DigiPaths
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